Process of precipitating and recovering metals.



C. H. URQUHART. PROCESS OF PREGIPITATING AND RECOVERING METALS. APPLIOATION FILED SEPT. 9, 1913.

1,090,661 Q Patented Mar. 17, 1914.

llllllllll PHI 1 UNITED STATES PATENT OFFICE.

CHARLES H. URQUHART, OF NEWARK, NEW JERSEY.

PROCESS OF PBECIPITATING AND RECOVERING METALS.

' Specification of Letters Patent. Patented Mar, 17, 19141 Continuation of application Serial No. 775,165,1iled March 1a, 1913. This application filed September a,

.1918. Serial No. 788,893.

To all whom it may concern:

Be it known that I, CHARLES H. URQU- HART, a citizen of the United States, and a resident of the city of Newark, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in the Process of Precipitating and Recovering Metals, of which the following is a specification.

This invention relates to metallurgical processes and more particularly to a process of recovering precious metals, especially gold and silver, from cyanid solutions.

The principal object of this invention is the recovery of precious metals in solution, by passing the solution through granulated zinc, and excluding the air from the granulated zinc during the passage of the solution.

Another object of this invention is the recovery of precious metals by passing the pregnant solution through granulated zinc, excluding air from the zinc, and agitating the mass, thereby causing the particles of the precious metals to be freed from the zinc and at the same time breaking up the granulated zinc to produce clean unoxidized'surfaces for further carrying on the process of precipitation.

Still other and further objects of this invention will in part be obvious, and will in part be pointed out in the specification hereinafter following by reference to the accompanying drawings.

This application is a continuation of my prior application bearing Serial No. 775,165, and filed March 18, 1913.

The figure of the drawing illustrates a preferred form of apparatus in which my process may becarried out. There may be other forms of devices, however, in which my process may be conducted.

Metallic zinc has long been known as being a good precipitant for precious metals from cyanid solutions, but its use heretofore has been attended with many difliculties. Zinc threads or shavings have been used, but the cost thereof is high, and even when packed tightly in boxes (the boxes are arranged in a stepped tandem series to successively treat the metal bearing solution) the shavings soon become polarized and coated and require frequent washing in order to enable the process to be continued with any degree of success. In practice the zinc shavlngs must be handled daily (in some m11ls weekly) thereby entailing conslderable manual labor. In the operation of the zinc shavings boxes there are formed what are known in the art as zinc' shorts. These zinc shorts constitute small parholes of zinc broken ofl from the shavings, and they settle to the bottom of the box thereby becoming covered with the precipitates and consequently are inactive. F urthermore, in the subsequent smelting of the prec pitates, these zinc shorts are verV detrimental in that they incur considerable expense by requiring a large amount of flux to be used. This difficulty is well known in the art, and it is customary, in orderto obvlate it, to give the precipitate containing zinc shorts a preliminary treatment with sulfuric acid to dissolve out the zinc. This treatment is, of course, expensive; furthermore, the. repeated handlings necessary mean a certain loss of the precious metals. It also happens, in the use of the zinc shav-' ings box process, that a large percentage of the precipitate clings to the coarse zinc particles in the box and consequently is not recovered during the ordinary working of the process. Zinc dust has also been used (known as zinc fume), but even this has many disadvantages. The zinc dust is costly. It must be stored and shipped in hermetically sealed containers, and as soon as a container is broken or opened the contents thereof must be used, otherwise the dust will oxidize, and oxidized zinc in a cyanid solution is very undesirable and detrimental. The extreme liability of zinc fume to oxidize renders it inflammable and explosive and therefore dangerous to handle and expensive to ship. This feature alone is of importance because most precious metal mines are more or less isolated and the question of shipping supplies 'is of great importance commercially. Zinc spheres in the form of shot have also been used as precipitants, but the smooth surfaces of'the spheres do not constitute good surfaces for causing the forming and effusion of hydrogen. The smooth surfaces are not the best sort of surfaces to carry on electro-chemlcal reactions.

In the commercial treatment of large quantities of metal bearing solution, to recover the precious metals therefrom there are two things that are especially desirable; first, a satisfactory precipitant, capable of being economically obtained, easy to transport, and safe to handle; second, a substantially continuous process for using said precipitant, said process requiring a minimum amount of manual labor, and skilled attendants, to carry out the process, and keep the precipitant inworking condition. I have discovered by experiment and study that granulated'zinc, prepared as describedbe' low, satisfies the first mentioned requirement, and that treatment of the pregnant solution by passing the same through a mass of the granulated zinc in a closed chamber entirelyfilled with solution, thereby excluding the air, and agitating the granulated zinc so as to grind or remove the precipitated metaland form minute zinc particles, satisfies the second requirement, for the reason thatwhen the process is so carried out it is unnecessary to re-handle the granulated zinc, and the whole process 1s continued, or

carried out, entirely by machinery instead of manual labor, and it does not require skilled attendants. And my process is free from the difliculties I have above referred to in connection with the art prior to my invention. a

The granulated zinc, to which I have referred as a precipitant, is prepared by melting common'pig. zinc, known in the art as spelter, heating the-melted zinc to a high temperature, but not suflicient tad-volatilize the same, then pouring the melted zinc from a height of 2 or 3' feet into a bath of cold water. The resulting product comprises comparatively small, irregular-,unoxidized masses of brittle zinc. This product is cheap to produce and may be handled without danger, since it is not inflammable nor explosive. Its irregular form affords a mass of zinc having ideal surfaces for precipitation-purposes, and for enabling the hydrogen to freely form and escape. The granulated .zinc produced in the manner prescribed, is not malleable, but is so brittle that when introduced into a revolving drum it breaks up into minute particles by attrition, without the use of abrasives, or without the necessity of-mixing other metals with the zinc to form a special alloy to secure the brittle product. Where metals are used to alloy the zinc to secure brittleness, these metals may not act as precipitants, but they 'tle flakes of irregular conformation.

do go into solution, and to this extent tend to use up, or foul, the cyanid solution, and

the'alloy is, of course, more expensive to produce than is the simple metal.

The term granulated zinc is sometimes loosely used to designate small round, or

substantially round, particles of zinc commonly called shot zinc. The product which I have herein designated as granulated zinc should not be confused with shot ZlIlC. Shot zinc is formed by permitting molten zinc at a comparatively low temperature, to fall into Water from a height that they be sufficiently cooled by falling through the air to prevent their being broken or shattered when they strike thewater. Itwill therefore be seen that shot zinc is not subjected to "a sudden and extreme chill when the metal reaches the water. My granulated zinc on the contrary, as prepared as abovespecified, results from .a very hot and fiuid'metal striking a chilling bath after a short afall. The metal being very limpid tends to spread out or splash when it strikes the cold Water, the result being that the thin layer of metal is thus formed into highly crystalline and e irregular formation of this materialrenders it especially good for electro-chemical ac tion and'it thereby forms a splendid precipitating medium. The-highly crystalline character of the particles renders the ma- I terial very'brittle so that when tumbled en masse in a rvoluble drum the particles break and thus-continuously form new surfaces for deposition of the precious metals. This breaking up of the particles is far more desirable and operatesfar more effectively than where masses of zinc are subjected to the action of an abrasive to secure new surfaces. I The action of an abrasive is never entirely perfect, whereas a break in the material leaves an absolutely clean' crystalline surface for further activity.

- In the-treatment of the pregnant solution with zinc, it is necessary to practical success that no-air be present, and therefore, I have found it convenient to carry out the process .in the following apparatus, which I will describe by referring to the drawings The granulated 'zinc is carried inthe revolving drum 1 and is introduced therein through the hand hole 2. The revolving .drum is provided at each end with headers 4', which carry screens 5 and 6, indicated diagrammatically in they drawings. These screens are for the obvious purpose of retaining the granulated zinc within the drum 1. Tubular shafts 7 and 8 are respectively carried by the headers 4, and when in position in the bearings 9 and 10, constitute the supports for the drum 1, and also constitute duets or conduits through which the pregnant solution is introduced into the drum. The tubular shaft 7 carries a large gear 11, which, cooperating with a suitable driving gear, not shown, comprises a means for rotating the drum to agitate the contents thereof.

a The shaft 7 terminates within a vertical inlet well 12, and a stufling box, or gland, 14, is provided to insure a running fluid tight joint where the shaft 7 enters the said well 12. This well 12 is provided with a suitable cleanout pipe 15. The shaft 8 terminates within an outlet well 16, which likewise is provided with a stufiing box 17 to also insure a fluid tight running joint. The outlet well -17 is provided, near the upper end thereof with an outlet pipe 18, and is provided at the lower'end with a suitable cleanout pipe 23. The lowest part of the opening in the outlet pipe 8 is ma horizontal line slightly above the highest part of the interior of the drum 1, which highest part is at the hand hole 2 when the drum is in the position indicated in the drawings.

In order to carry out my process the granulated zinc is prepared as I have specified, the drum is revolved until the hand hole is at the highest position, as indicated by the drawings, the hand hole cover removed, and the drum partly filled with the granulated zinc. The pregnant solution is then run into theinlet well 12, and, of course, from the well into the drum 1 until the drum is entirely filled. The filling of the drum will take place before any solution will flow out of the outlet pipe 18 for the reason that, as has been explained, this outlet pipe is slightly higher than the highest point in the drum. The hand hole cover is then replaced and the apparatus is ready to carry out the process. I

As the drum 1 is slowly revolved by the gear 11, and cooperating driving mechanism, the brittle granulated zine will be broken up by abrasion or attrition. The breaking up of the brittle zinc particles takesplace under the solution within the revolving drum 1, from which the air is entirely excluded, and therefore produces small particles of zinc having clean, fresh, irregular surfaces which are entirely free from oxid since they are produced free from oxidizing conditions. The process may be carried on substantially continuously, it only being necessary to occasionally add granulated zine to the drum to take the place of such zinc. particles as are consumed. The abrading action of the zinc particles frees the precipitated precious metal, gold or silver, which for the greater part is .carried off by the solution in suspension and may be removed by any suitable device. For example, the outlet pipe 18 may discharge into a settling tank 19, provided with bafiles 20, and having asloping bottom 21, where the most of the precipitated metal ing and filtering material, and may eventually pass into a still further filtering ehamber 25 which is preferably charged with a combustible filtering material. The final clear liquor is conveniently drawn offv through a proper pipe or duct 26 and may then be used for another cycle of operations.

Since the invention as set forth herein relates entirely to a process, I desire it to be understood that the apparatus illustrated and described is merely for illustrative purposes, and that my process may be carried out in many widely different sorts of devices which specifically form no part of the present invention.

Whenever the term zinc is used herein it is intended also to include commercial zinc, known in the art as spelter.

Having thus described my invention what I claim i's,-

1. The process of precipitating and recovering metals from solution, which consists in passing the pregnant solution into and through a mass of specified granulated zinc in a closed chamber, the pregnant solution entirely filling the said chamber, thereby excluding air from the granulated Linc; agitating the solution and granulated zine to free the precipitated metals from the zinc by "abrasion; then separating the free metal particles from the solution.

2. The process of precipitating and recovering metals from solution, which consists in submerging a mass of specified granulated zinc by the pregnant solution; comminuting the granulated zine while so submerged, thereby also freeing the precipitated metal; and then recovering the free metal from solution.

3. The process of precipitating and recovering metals from solution, which consists in submerging a mass of specified granulated 'zinc by a substantially continuous flow of pregnant solution; agitating the mass of granulated. zine during the flow of the pregnant solution to free the precipitated metal, then recovering the free metal from the solution.

4. The process of precipitating and recovering metals from solution, which consists in passing the solution through granulated zinc repaired as specified; excluding air from said granulated zinc during the passing of said solution; agitating said granulated zinc to produce a grinding action between the particles; then separating the free metal particles from the solution; j

' 5.- The process of recipitatin and, recov- 5 ering metals from so ution, whic consists in passing the metal bearing solution into a mass of granulated zmc repaired as speclfied; excludlng all from sald granulated zinc when the solution is present; agitating the granulated zinc to remove the precipi- 10 tated metals by abrasion; then separating the free metal articles from the solution. Y

OH RLES H. URQUHART. Witnesses:

GEORGE W; RAMsEY, EDITH C. RAMsnY. 

